Examples of an electronic device that can be used as a frequency filter or a resonator include a surface acoustic wave (SAW) device. The surface acoustic wave device is configured by forming an interdigital electrode formed of a metal film that excites a surface acoustic wave, such as an aluminum film, on a surface of a monocrystal substrate having piezoelectric properties, such as a lithium tantalate (LiTaO3) or a lithium niobate (LiNbO3) substrate.
Because the surface acoustic wave device can be miniaturized, with further reduction of mobile communication equipment including portable telephones in size in recent years, the surface acoustic wave device has been used as a duplexer for taking an electric signal in a certain frequency band from a received wave or a transmitted wave in the mobile communication equipment.
When used as the duplexer equipped in the portable telephone, the surface acoustic wave device necessarily inputs/outputs and processes high frequencies, requiring a high power durability. To satisfy this requirement, Patent document 1 discloses a technique of improving the power durability of the surface acoustic wave device. Specifically, Patent document 1 discloses that a piezoelectric monocrystal substrate having a cut angle in a specific range is adopted, a titanium nitride layer is laminated on the substrate and then, an aluminum layer that serves as an electrode layer is further formed thereon by epitaxial growth. This can form an electrode having no grain boundary, thereby improving the power durability.
[Patent document 1] Unexamined Patent Publication No. 2003-101372
However, the above-mentioned surface acoustic wave device disclosed in Patent document 1 has a problem that the cut angle of the piezoelectric monocrystal substrate used in the surface acoustic wave device is limited. That is, the crystal structure of the surface of the piezoelectric monocrystal substrate needs to match that of the titanium nitride layer and thus, the piezoelectric monocrystal substrate having a specific cut angle must be used. When the piezoelectric monocrystal substrate having the specific cut angle is not used, the power durability of the surface acoustic wave device disadvantageously lowers, resulting in quality deterioration.